X-ray tubes are for bringing electrons emitted from an electron gun into collision with a target to generate X-rays. One of conventional X-ray tubes is described in Patent Document 1, for example. This X-ray tube includes a vacuum enclosure with a valve joining the enclosure main body for housing an electron gun, in the vacuum enclosure inserted is a target support body for supporting a target therein. The valve is formed with an inner cylindrical portion in a way that the leading end portion thereof is folded wholly inward, and the leading end portion of the inner cylindrical portion is fixed to the target support body. Then, the target support body is provided with a cover for covering the fixation portion where the target support body and the leading end portion of the inner cylindrical portion are fixed to each other to suppress the generation of discharge in the valve.    Patent Document 1: U.S. Pat. No. 5,077,771